CN108900099B

CN108900099B - Microwave frequency conversion circuit and control method thereof

Info

Publication number: CN108900099B
Application number: CN201810717689.8A
Authority: CN
Inventors: 顾永德; 戴训江; 赵志刚
Original assignee: MOSO POWER SUPPLY TECHNOLOGY Co Ltd; Processing Technology Co Ltd
Current assignee: Moso Power Supply Technology Co ltd
Priority date: 2018-07-03
Filing date: 2018-07-03
Publication date: 2020-01-03
Anticipated expiration: 2038-07-03
Also published as: CN108900099A

Abstract

The invention discloses a microwave frequency conversion circuit, which comprises a rectification circuit for rectifying an alternating current power supply, an inverter circuit for converting a first direct current power supply into a second alternating current power supply, a power conversion control circuit for controlling the power of the second alternating current power supply output by the inverter circuit under the control of a control signal provided by a control circuit, a first voltage detection circuit for detecting the first alternating current power supply, and a first current detection circuit for detecting the current of the first direct current power supply, wherein the control circuit adjusts the control signal according to the phase difference of the zero crossing point of the voltage and the current of the first alternating current power supply, which is obtained by detection, so as to correct the power factor of the second alternating current voltage. Further provides a control method of the microwave frequency conversion circuit.

Description

Microwave frequency conversion circuit and control method thereof

Technical Field

The invention relates to the technical field of microwave ovens, in particular to a technology of a variable-frequency microwave power supply circuit of a microwave oven, and specifically relates to a microwave frequency conversion circuit and a control method of the microwave frequency conversion circuit.

Background

In the microwave oven, a magnetron is driven by a frequency conversion circuit to release microwave energy, so that articles such as food and the like are heated. In addition, the magnetron is also applied to industrial microwave power heating and sterilizing equipment.

The frequency conversion circuit and the magnetron form a frequency conversion microwave power supply, wherein the output voltage and current of the frequency conversion circuit meet the requirement of normal work of the magnetron, and meanwhile, power factor correction is required to be carried out aiming at the input voltage so as to improve the effective utilization rate of the power supply.

However, when performing power factor correction, the voltage and current are usually collected and detected for the dc power supply after the ac voltage rectification, that is, the ac power supply directly received by the current and voltage driving circuit for power factor correction is often affected by the rectification circuit. Therefore, the power factor correction is also affected by the electronic components in the rectifier circuit, so that the power factor correction cannot achieve the best effect.

Disclosure of Invention

In order to solve the problems in the prior art, the invention provides a microwave frequency conversion circuit for performing accurate correction on an input power supply and a control method thereof.

The embodiment of the invention provides a microwave frequency conversion circuit, which comprises:

the rectifier circuit receives a first alternating current power supply through an alternating current input end comprising a first input end and a second input end and converts the first alternating current power supply into a first direct current power supply;

the inverter circuit is electrically connected with the rectifying circuit and is used for converting the first direct-current power supply into a second alternating-current power supply and providing the second alternating-current power supply for a magnetron;

the power conversion control circuit is electrically connected with the rectifying circuit and the inverter circuit and is used for controlling the power of the second alternating current power supply output by the inverter circuit according to a control signal provided by the control circuit;

the first voltage detection circuit is used for detecting the first alternating current power supply and outputting a first voltage detection signal according to a detection result, wherein the first voltage detection signal represents a phase of a voltage of the first alternating current power supply, and the phase of the voltage comprises a zero crossing point;

the first current detection circuit is electrically connected with the rectifying circuit and the power conversion control circuit, and is used for detecting the current of the first direct current power supply and correspondingly outputting a first current detection signal, wherein the first current detection signal represents the phase of the current of the first alternating current power supply, and the phase of the current comprises a zero crossing point;

the control circuit is electrically connected with the power conversion control circuit, the first voltage detection circuit and the first current detection circuit, and the control circuit identifies a phase difference of zero-crossing points in the phases of the voltage and the current according to the first voltage detection signal and the first current detection signal and outputs the control signal according to the phase difference to correct the power factor of the first alternating current power supply.

The embodiment of the invention provides a control method of the microwave frequency conversion circuit, which comprises the following steps:

receiving a first alternating current power supply from an alternating current input end, converting the first alternating current power supply into a first direct current power supply, converting the first direct current power supply into a second alternating current power supply for supplying power to a magnetron, and simultaneously controlling the power of the second alternating current power supply through a control signal;

performing PID power factor adjustment for a first AC power source, the PID power factor comprising the steps of:

acquiring a zero crossing point of voltage and a zero crossing point of current of a first alternating current power supply to calculate a detection phase difference of the voltage and the current of the first alternating current power supply, and calculating a detection power factor according to the detection phase difference;

determining a second difference between the detected power factor and the maximum power factor;

and when the second difference value is within a first preset power factor range, adjusting the duty ratio of the updating control signal so as to adjust the power factor of the first alternating voltage.

Compared with the prior art, the voltage and phase of the first alternating current power supply received by the alternating current input end are detected directly, so that the voltage and the zero crossing point of the first alternating current power supply can be obtained more accurately, the phase difference between the voltage and the current of the first alternating current power supply is accurately identified, and more accurate power factor adjustment is performed according to the phase difference.

Drawings

In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.

Fig. 1 is a circuit block diagram of a microwave frequency conversion circuit according to a first embodiment of the present invention;

FIG. 2 is a schematic diagram of a specific circuit structure of the microwave frequency conversion circuit shown in FIG. 1;

FIG. 3 is a schematic diagram of a specific circuit structure of the first voltage detection circuit shown in FIG. 2;

fig. 4 is a circuit block diagram of a microwave frequency conversion circuit according to a second embodiment of the present invention;

fig. 5 is a specific circuit structure diagram of the first protection unit and the first feedback detection unit in the microwave frequency conversion circuit shown in fig. 4 in the first embodiment;

fig. 6 is a specific circuit structure diagram of a second embodiment of a first protection unit and a first feedback detection unit in the microwave frequency conversion circuit shown in fig. 4;

fig. 7 is a specific circuit structure diagram of a third embodiment of the first protection unit and the first feedback detection unit in the microwave frequency conversion circuit shown in fig. 4;

FIG. 8 is a flow chart of the operation of the microwave frequency conversion circuit shown in FIGS. 1-7;

FIG. 9 is a flowchart illustrating the detailed steps of the magnetron preheating control shown in FIG. 8;

FIG. 10 is a schematic flow chart showing the specific steps of proportional forward regulation of the magnetron input power shown in FIG. 8;

FIG. 11 is a schematic flow chart illustrating the specific steps of PID power adjustment of the magnetron shown in FIG. 8;

FIG. 12 is a schematic flow chart illustrating the specific steps of PID power factor adjustment for the magnetron row shown in FIG. 8;

FIG. 13 is a flowchart illustrating the specific steps of the protection logic executed when an abnormal condition occurs in the magnetron shown in FIG. 8.

Detailed Description

The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

Please refer to fig. 1, which is a circuit block diagram of a microwave frequency conversion circuit 10 according to a first embodiment of the present invention. As shown in fig. 1, the microwave frequency conversion circuit 10 includes: the power supply device comprises an alternating current input terminal Vin, a rectifying circuit 11, a power conversion control circuit 12, an inverter circuit 13, a first voltage detection unit 14, a first current detection circuit 15, a control circuit 16, a magnetron 17 and a communication circuit CM.

The ac input terminal Vin is configured to receive a first ac power supply, where the first ac power supply is an ac mains supply of 220V and 50Hz, the ac input terminal Vin includes a first high-voltage terminal L1, a first low-voltage terminal N, and a ground protection terminal PE, and the ac mains supply is input into the microwave frequency conversion circuit 10 through the three ports.

The rectifying circuit 11 is electrically connected to the ac input terminal Vin and is configured to shape and convert a first ac power into a first dc power.

The inverter circuit 13 is configured to convert the received first dc power into a second ac power by inverting the voltage, and control the voltage of the second ac power to be several times of the voltage of the first dc power, and the second ac power is provided to the magnetron 17 electrically connected to the inverter circuit 13. The magnetron 17 may be an electric vacuum device for generating microwave energy used in heating equipment such as a microwave oven for generating heat or other applications.

The power conversion control circuit 12 is electrically connected to the inverter circuit 13, and is configured to control the power of the second ac power source output by the inverter circuit 13.

The first voltage detecting unit 14 is electrically connected to the first high voltage terminal L1 and the first low voltage terminal N, and configured to detect the first ac power and output a first voltage detecting signal according to a detection result, so as to identify a voltage of the first ac power and a voltage zero crossing point of the first ac power. That is, the first voltage detection signal is indicative of a phase of a voltage of the first ac power source, the phase of the voltage including a zero-crossing point.

The first current detection circuit 15 is electrically connected to the rectification circuit 11, the power conversion control circuit 12 and the first voltage detection circuit 14, and the first current detection circuit 15 is configured to detect a current of the first dc power supply and correspondingly output a first current detection signal. Wherein the first current detection signal is indicative of a phase of a current of the first AC power source, the phase of the current including a zero crossing.

The control circuit 16 is electrically connected to the power conversion control circuit 12, the first voltage detection circuit 14 and the first current detection circuit 15, and the control circuit 16 is configured to output a control signal to the power conversion control circuit 12 according to the first voltage detection signal and the first current detection signal, so that the power conversion control circuit 12 adjusts the frequency and the power of the second ac power source output by the inverter circuit 13. In this embodiment, the control signal is a Pulse Width Modulation (PWM) signal.

The communication circuit CM is electrically connected to the control circuit 16, and the control circuit 16 transmits the state of the microwave frequency conversion circuit to the external circuit through the communication circuit CM.

More specifically, please refer to fig. 2, which is a schematic circuit diagram of the microwave frequency conversion circuit 10 shown in fig. 1.

The rectifying circuit 11 includes a first rectifying input end 111, a second rectifying input end 112, and a third rectifying input end 113, which are respectively and sequentially electrically connected to the first high-voltage end L1, the first low-voltage end N, and the ground protection end PE, and are configured to receive a first ac power.

The rectifier circuit 11 further includes a rectifier bridge 114, a first DC inductor L1, a first smoothing capacitor C1, a second smoothing capacitor C2, a first rectifier output terminal DC + and a second rectifier output terminal DC-.

The rectifier bridge 114 is electrically connected to the first rectifier input end 111, the second rectifier input end 112, and the third rectifier input end 113, and performs rectification for the first ac power and outputs the first DC power, the first filter capacitor C1 is electrically connected between the high voltage end VG and the low voltage end VL of the rectifier bridge 114, the first DC inductor L1 is electrically connected between the high voltage end VG and the first rectifier output end DC +, the second filter capacitor C2 is electrically connected between the first rectifier output end DC + and the low voltage end VL of the rectifier bridge 114, and the low voltage end VL is also directly electrically connected to the second rectifier output end DC-. In this embodiment, the high-voltage terminal VG and the low-voltage terminal VL form a port of the rectifier bridge 114 for outputting the first dc power, the low-voltage terminal VL is a ground reference voltage of 0V, and the voltage of the high-voltage terminal VG is higher than the reference voltage of the low-voltage terminal VL.

It should be noted that a path between the High-voltage terminal VG of the rectifier bridge 114 and the first rectification output terminal DC + is referred to as a High-side (High side) of the DC bus, and a path between the Low-voltage terminal VL of the rectifier bridge 114 and the second rectification output terminal DC-is referred to as a Low side (Low side) of the DC bus.

It is understood that the first rectified output terminal DC + and the second rectified output terminal DC-cooperate with each other to output the first DC power.

The inverter circuit 13 includes a transformer 131 and a voltage doubler circuit 133 electrically connected to the transformer 131.

The transformer 131 includes a first primary input terminal 1311, a second primary input terminal 1312, a first secondary output terminal 1313, a second secondary output terminal 1314, a third secondary output terminal 1315, a fourth secondary output terminal 1316, a primary winding W1, a first secondary winding W2, and a second secondary winding W3.

The first primary input terminal 1311 is electrically connected to the first and second rectification output terminals DC + and DC-respectively through two capacitors (not shown), and the second primary input terminal 1312 is electrically connected to the power conversion circuit 12.

The primary winding W1 is connected between the first primary input terminal 1311 and the second primary input terminal 1312 to receive a first dc power.

The first secondary winding W2 is connected between the first secondary output terminal 1313 and the second secondary output terminal 1314, and the second secondary winding W3 is connected between the third secondary output terminal 1315 and the fourth secondary output terminal 1316, i.e., the first secondary winding W2 is connected in series with the second secondary winding W3.

The transformer 131 receives a first dc power through the primary winding W1 and then transmits the first dc power to the first secondary winding W2 and the second secondary winding W3, so as to convert the first dc voltage into a second ac power, and further, the electromagnetic induction effect from the first secondary output terminal 1313, the second secondary output terminal 1314, the third secondary output terminal 1315, and the fourth secondary output terminal 1316 is output to the magnetron 17.

The transformer 131 further includes an iron core (not labeled) between the primary and secondary windings.

The voltage doubling circuit 133 includes a first high voltage diode DH1, a second high voltage diode DH2, a first high voltage capacitor CH1 and a second high voltage capacitor CH2 electrically connected between the second secondary winding W3 and the anode of the magnetron 17. The first high voltage diode DH1 is electrically connected between the second secondary output end 1314 and the third secondary output end 1315, and the second high voltage diode DH2 is electrically connected between the third secondary output end 1315 and the ground GND. The first high-voltage capacitor CH1 is electrically connected between the second secondary output end 1314 and the fourth secondary output end 1316, and the second high-voltage capacitor CH2 is electrically connected between the fourth secondary output end 1316 and the ground GND.

The voltage doubling circuit 133 performs voltage doubling processing, that is, boosting processing of preset multiples, on the second ac power output by the transformer 131 through the first high-voltage diode DH1, the second high-voltage diode DH2, the first high-voltage capacitor CH1, and the second high-voltage capacitor CH 2.

The magnetron 17 includes an anode 171, a cathode 172, and a filament winding 173, wherein the anode 171 is connected to a ground GND, that is, the anode 171 is electrically connected to a second high voltage diode DH2 and a second high voltage capacitor CH 2. The cathode 172 is electrically connected to the first secondary output 1313 and the filament winding 173 is electrically connected to the second secondary output 1314. To this end, the magnetron 17 receives the voltage-doubled second ac power from the first and second secondary windings W2 and W3 of the transformer 131 and the voltage-doubling circuit 133 through the anode 171, the cathode 172, and the filament winding 173, and heats and discharges the microwaves by being driven by the voltage-doubled second ac power.

The power conversion control circuit 12 includes a frequency conversion control unit 121 and a frequency conversion execution unit 123. The frequency conversion control unit 121 is configured to output a frequency conversion signal to the frequency conversion execution unit 123 according to a control signal, so that the frequency conversion execution unit 123 adjusts the operating frequency of the inverter circuit 13.

In this embodiment, the frequency conversion control unit 121 may be an Insulated Gate Bipolar Transistor (IGBT), which is a composite fully-controlled voltage-driven power semiconductor device composed of a BJT (Bipolar Junction Transistor) and an Insulated Gate field effect Transistor. The frequency conversion control unit 121 is configured to output a frequency conversion control signal, where the frequency conversion control signal is two pulse signals with opposite phases and the same duty ratio.

The variable frequency execution unit 123 includes a first switching transistor Q1 and a second switching transistor Q2 connected in series between the first rectified output terminal DC + and the second rectified output terminal DC-and connected in series with each other. The first switch transistor Q1 and the second switch transistor Q2 conduct and cut off corresponding frequencies according to the proportion of high and low electric potentials in the frequency conversion control signal under the control of the frequency conversion control signal.

Specifically, the first switching transistor Q1 includes a first switch control terminal CC1, a first conductive terminal EC1, and a second conductive terminal EC2, and the second switching transistor Q2 includes a second switch control terminal CC2, a third conductive terminal EC3, and a fourth conductive terminal EC 4.

The first switch control terminal CC1 and the second switch control terminal CC2 are electrically connected to the variable frequency control unit 121 at the same time, and respectively receive two pulse signals with opposite phases and the same duty ratio; the first conductive terminal EC1 is electrically connected to the first rectification output terminal DC +, the second conductive terminal EC2 is electrically connected to the third conductive terminal EC3, and the second conductive terminal EC2 and the third conductive terminal EC3 are simultaneously electrically connected to the second primary side input terminal 1312 of the inverter circuit 13; the fourth conductive terminal EC4 is electrically connected to the second rectified output terminal DC-.

Thus, the first switching transistor Q1 and the second switching transistor Q2 are alternately turned on and off under the control of two pulse signals having opposite phases and the same duty ratio, and thus, the frequency at which the first switching transistor Q1 and the second switching transistor Q2 are turned on and off can be controlled by the duty ratio of the pulse signals, and the input power of the second ac power source is adjusted.

In this embodiment, the first switch transistor Q1 and the second switch transistor Q2 are MOS transistors, the first switch control terminal CC1 and the second switch control terminal CC2 are gates of the MOS transistors, the first conductive terminal EC1 and the third conductive terminal EC3 are drains of the MOS transistors, and the second conductive terminal EC2 and the fourth conductive terminal EC4 are sources of the MOS transistors.

The first current detecting circuit 15 includes a current detecting resistor Rls and a current processing circuit 151, wherein the current detecting resistor Rls is electrically connected between the low voltage terminal VL and the second rectification output terminal DC-, and is configured to load a current corresponding to the first ac power in real time; the current processing circuit 151 performs amplification, digital sampling, filtering, and effective value (RMS) calculation on the current applied through the current detection resistor Rls, thereby obtaining a first current detection signal corresponding to an effective value of the input current of the first ac power source. The first current detection signal includes a current magnitude and a phase of the first ac power.

Please refer to fig. 3, which is a schematic circuit diagram of the first voltage detecting unit 14 shown in fig. 2.

The first voltage detection unit 14 includes a first voltage detection circuit 141 and a zero-cross detection circuit 143.

The first voltage detection circuit 141 includes: a first detection terminal P1, a second detection terminal P2, and a first differential operational amplifier OP 1.

The first detection terminal P1 and the second detection terminal P2 are electrically connected to the first high voltage terminal L1 and the first low voltage terminal N, respectively.

The first differential operational amplifier OP1 comprises a first non-inverting input terminal IN1, a first inverting input terminal IN2 and a first amplifying output terminal OUT1, wherein the first non-inverting input terminal IN1 is electrically connected to the first detecting terminal P1 through at least one first detecting resistor R1; the first inverting input terminal IN2 is electrically connected to the second input terminal P2 through at least one second sensing resistor R2, and the first inverting input terminal IN2 is electrically connected to the first amplifying output terminal OUT1 through a feedback amplifying unit F1.

IN this embodiment, the first non-inverting input terminal IN1 is electrically connected to the first detecting terminal P1 through three first detecting resistors R1, and the first non-inverting input terminal IN1 is further connected to a 2.5V reference power source through a resistor and a capacitor.

The first inverting input terminal IN2 is electrically connected to the second input terminal P2 through three second sensing resistors R2. The feedback amplifying unit F1 includes a first feedback resistor RF1 and a first feedback capacitor CF1 connected in parallel to each other.

The first differential operational amplifier OP1 converts the first ac power source into a sinusoidal first voltage detection signal according to a first ratio, the first voltage detection signal being indicative of the voltage of the first ac power source.

In addition, a power supply terminal (not labeled) of the first differential operational amplifier OP1 is connected to the 5V driving power supply through a capacitor, and a ground terminal of the first differential operational amplifier OP1 is connected to the ground reference terminal.

The zero-cross detection circuit 143 includes a zero-cross comparator OP 2. The zero-crossing comparator OP2 includes a second non-inverting input terminal IN3, a second inverting input terminal IN4, and a first comparing output terminal OUT 2.

The second non-inverting input terminal IN3 is electrically connected to the first amplifying output terminal OUT1 through a third detecting resistor R3, and the second non-inverting input terminal IN3 is electrically connected to the first comparing output terminal OUT2 through a second feedback resistor RF 2.

The second inverting input terminal IN4 is electrically connected to the first reference voltage through the fourth sensing resistor R4. In this embodiment, the first reference voltage is 2.5V.

The first comparison output terminal OUT2 is electrically connected to the second reference voltage through a reference resistor RC 1. In this embodiment, the second reference voltage is 5V.

The zero-cross detection circuit 143 is configured to compare the first ac voltage detection signal with a first reference voltage, and output a potential signal with a phase opposite to that of the previous time period from the first comparison output terminal OUT2 when the first ac voltage detection signal is smaller than the first reference voltage, so that when the phase of the first ac voltage detection signal of the ac signal is opposite to that of the first reference voltage and smaller than the first reference voltage, a first square-wave pulse signal with a second reference voltage can be output. Wherein the first square wave pulse signal is in phase with the first voltage detection signal and is used to characterize a zero crossing of the first voltage detection signal.

The first voltage detection circuit 141 measures the voltage of the first ac power source accurately and provides a first voltage detection signal that represents the first ac power source accurately, that is, the first voltage detection circuit 141 outputs a small sinusoidal signal including a zero-crossing point, and then the zero-crossing detection circuit 143 can generate a steep-edged square-wave pulse signal at a zero-crossing point of the small sinusoidal signal as the first voltage detection signal, so that noise interference can be eliminated effectively, and the first voltage detection signal that represents the voltage and phase of the first ac power source accurately is obtained finally.

The phase difference between the zero-crossing points of the voltage and the current of the first ac power source obtained by the first voltage detection circuit 141 and the zero-crossing detection circuit 143 can adjust the voltage or the current phase of the first ac power source by adjusting the frequency and the duty ratio of the control signal output by the control circuit 16, thereby performing the correction adjustment on the power factor of the first ac voltage.

Please refer to fig. 4, which is a circuit block diagram of a microwave frequency conversion circuit according to a second embodiment of the microwave frequency conversion circuit of the present invention.

As shown in fig. 4, in the present embodiment, the microwave frequency conversion circuit 20 and the microwave frequency conversion circuit 10 have substantially the same circuit structure, except that the microwave frequency conversion circuit 20 further includes a first protection unit 28, a first feedback detection unit FM1 and a temperature sensing unit 29 compared to the microwave frequency conversion circuit 10.

The first protection unit 28 is configured to detect a high-side current of the dc bus, and output the high-side current of the dc bus obtained according to the detection to the control unit 26, and when the high-side current of the dc bus exceeds a high-side current threshold, the control circuit 26 controls the inverter circuit 23 to stop converting the first dc power supply into the second ac power supply. The first feedback detection unit FM1 is used to detect the load current of the magnetron 27, and when the load current exceeds a load current threshold, the control circuit 26 controls the inverter circuit 23 to stop converting the first dc power into the second ac power.

The temperature sensing unit 29 is used for sensing the temperature of the magnetron 27, wherein the temperature sensing unit 29 may be a temperature sensor or a thermal relay. When the temperature of the magnetron 27 is greater than the load temperature threshold, the control circuit 26 controls the inverter circuit 23 to stop converting the first dc power into the second ac power, and at the same time, the temperature sensing unit 29 controls the magnetron 27 to pause.

The circuit structures of the first protection unit 28 and the first feedback detection unit FM1 in the microwave frequency conversion circuit 20 shown in fig. 4 are specifically illustrated and described below with reference to fig. 5 to 7, respectively.

Please refer to fig. 5, which is a specific circuit structure diagram of the first protection unit 28 and the first feedback detection unit FM1 in the microwave frequency conversion circuit 20 shown in fig. 4.

Specifically, as shown in fig. 5, the first protection unit 28 includes a first shunt resistor RS1, and the first shunt resistor RS1 is electrically connected between the first rectification output terminal DC + of the rectification circuit and the inverter 23.

A first feedback detection unit FM1 for detecting the current flowing through the magnetron 27 and feeding back the detection result to the control circuit 26. The first feedback detection unit FM1 includes a second shunt resistor RS2, wherein the second shunt resistor RS2 is electrically connected between the second high-voltage capacitor CH2 and the ground GND.

Please refer to fig. 6, which is a specific circuit structure diagram of the second embodiment of the first protection unit 28 and the first feedback detection unit FM1 in the microwave frequency conversion circuit 20 shown in fig. 4.

Specifically, as shown in fig. 6, the first protection unit 28 includes a first current mutual inductance element TA1, and the first current mutual inductance element TA1 is electrically connected between the first rectification output terminal DC + of the rectification output circuit and the inverter 23.

Please refer to fig. 7, which is a specific circuit structure diagram of the third embodiment of the first protection unit 28 and the first feedback detection unit FM1 in the microwave frequency conversion circuit 20 shown in fig. 4.

Specifically, as shown in fig. 7, the first feedback detection unit FM1 includes a second current transformer TA2, wherein the second current transformer TA2 is electrically connected between the first high-voltage capacitor CH1 and the second high-voltage capacitor CH 2.

Please refer to fig. 8, which is a flowchart illustrating a control method of the microwave frequency converter circuit 10-20 shown in fig. 1-7 during operation.

As shown in fig. 8, the control method of the microwave frequency conversion circuit 10-20 at least includes the following steps:

in step 1, the rectifying circuit 11 receives a first ac power from the ac input terminal Vin and converts the first ac power into a first dc power, and converts the first dc power into a second ac power for supplying power to the magnetron 17, and drives the magnetron 17 to preheat.

And 2, when the preheating of the magnetron 17 reaches the preset duration, the input power is adjusted in a forward direction according to the proportion.

And 3, after the input power reaches the preset power, performing PID (proportion-integration-differentiation) power regulation on the first alternating current power supply.

And 4, after the input power is subjected to PID power regulation, PID power factor regulation is carried out on the input power.

Preferably, if an abnormal condition occurs in any one of the steps 1-4, the protection logic of step 5 is executed for the microwave power circuit, where the abnormal condition at least includes: the protection logic is that the power conversion control circuit controls the inverter circuit to stop the inverter conversion aiming at the first direct current power supply.

Specifically, referring to fig. 8 and 9 together, fig. 9 is a flowchart illustrating the specific steps of the magnetron preheating control in step 1 shown in fig. 8.

As shown in fig. 9, the magnetron preheating control includes at least the following steps:

and 11, converting the first direct current power supply into a second alternating current power supply according to the first resonant frequency.

Specifically, the control circuit 16 provides a control signal with a first duty ratio and an initial frequency to the variable frequency control unit 121 in the power conversion control circuit 12, and the variable frequency control unit 121 outputs two variable frequency control signals of pulse signals with opposite phases and the same duty ratio to the 2 switching transistors Q1, Q2 in the power conversion control circuit 123, so that the switching transistors Q1, Q2 perform on and off at the initial frequency and for a duration corresponding to the first duty ratio, and further the first dc power source is converted into the second ac power source according to the first resonant frequency.

And step 12, detecting and acquiring the voltage Urms and the current Irms of the first alternating current power supply, and calculating the first alternating current input power Pin according to the voltage Urms and the current Irms of the first alternating current power supply.

Specifically, the voltage supplied from the ac input terminal Vin to the first ac power is obtained by the first voltage detection circuit 141 in the first voltage detection unit 14, and the current corresponding to the first ac power is obtained by the first current detection circuit 15.

And step 13, when the first alternating current input power Pin is greater than the preheating power, increasing the frequency of the control signal according to a fixed step length, and when the first alternating current input power Pin is less than the preheating power, reducing the frequency of the control signal according to the fixed step length.

That is, the control circuit 16 increases or decreases the frequency of the control signal outputted therefrom in fixed steps, thereby controlling the on and off frequencies of the 2 switching transistors.

And step 14, when the first alternating current input power Pin is equal to the preheating power, judging whether the preheating time is longer than a preset time Tf, when the preheating time is longer than the preset time Tf, executing proportional forward adjustment on the input power in the step 2, and when the preheating time is shorter than the preset time Tf, judging whether the microwave frequency conversion circuits 10 and 20 are abnormal or not.

Step 15, when the microwave frequency conversion circuits 10 and 20 are abnormal, executing a protection logic 5; when the microwave frequency conversion circuit 10 is not in an abnormal condition, the switching control element is continuously controlled according to the first duty ratio to execute the on-off action according to the first frequency, so that the preheating process is executed for the

magnetrons

17 and 27 until the preheating time is longer than the preset time length, and the completion of the preheating of the

magnetrons

17 and 27 is represented.

By controlling the input power and time in the preheating process, the overcharge and oscillation of the

magnetrons

17 and 27 caused by overlarge input power in the preheating process can be effectively avoided, the power stability of the magnetrons is maintained, and the service life of the magnetrons is prolonged.

Specifically, referring to fig. 8 and 10 together, fig. 10 is a flowchart illustrating the specific steps of the step 2 shown in fig. 8, in which the magnetron input power is adjusted in the forward direction according to the ratio.

As shown in fig. 10, the proportional forward adjustment of the input power of the magnetron in step 2 at least includes the following steps:

and step 21, converting the first direct-current power supply into a second alternating-current power supply according to the first resonant frequency, acquiring the voltage Urms and the current Irms of the first alternating-current power supply, and calculating the first alternating-current input power Pin according to the voltage Urms and the current Irms of the first alternating-current power supply.

And step 22, judging the magnitude of the first alternating current input power Pin and a preset target power Prf.

And step 23, when the first alternating current input power is greater than or equal to a preset target power Prf, completing the forward regulation of the input power proportion.

And 24, when the first alternating current input power is smaller than the preset target power Prf, reducing the frequency of the control signal according to a fixed step length.

And step 25, when the microwave frequency conversion circuit 10 has an abnormal condition, executing protection logic.

By carrying out forward adjustment of the input power according to the proportion, the first alternating current input power Pin of the first alternating current voltage can gradually reach a preset target power according to a fixed step length, and overshoot or oscillation of the input power is avoided.

Specifically, referring to fig. 8 and fig. 11 together, fig. 11 is a flowchart illustrating the specific steps of the step 3 of the PID power adjustment of the magnetron shown in fig. 8.

As shown in fig. 11, the PID power adjustment of the magnetron row in step 3 at least includes the following steps:

and step 31, converting the first direct current power supply into a second alternating current power supply according to the first resonant frequency.

And step 32, acquiring the voltage Urms and the current Irms of the first alternating current power supply, and calculating the first alternating current input power Pin according to the voltage Urms and the current Irms of the first alternating current power supply.

Step 33, determining whether a first difference Δ P between the first ac input power Pin and a preset target power P _ set is within a first threshold range Pref, where in the time period t, the first difference Δ P (t) is Pin-P _ set, Pin is the first ac input power, and P _ set is the preset target power.

And step 34, when the first difference value Δ P is within the first threshold range Pref, performing the PID power factor adjustment in step 4.

And step 35, when the first difference value Δ P exceeds the first threshold range Pref, adjusting the frequency of the control signal, wherein the frequency of the control signal is adjusted according to the first difference value Δ P (t) of two adjacent time periods before the current time period.

Specifically, Δ P (a) · Δ P (t) -B · Δ P (t-1) + C · Δ P (t-2), Δ f ═ D · Δ P, where A, B, C, D is a constant, t is a time period corresponding to one of the signal cycles of the control signal, and at time t-1, Δ P (t-1) ═ Δ P (t); at time t-2, Δ P (t-2) ═ Δ P (t-1).

Then, in the t period, Fsw (t) corresponding to the updated control signal is Fsw (t-1) +. Δ f, where Fsw (t-1) is the frequency of the control signal corresponding to the t-1 period.

And step 36, when the microwave frequency conversion circuit 10 has an abnormal condition, executing protection logic.

Specifically, referring to fig. 8 and 12 together, fig. 12 is a flowchart illustrating the specific steps of the step 4 magnetron line PID power factor adjustment shown in fig. 8.

As shown in fig. 12, the PID power factor adjustment of magnetron rows in step 4 at least includes the following steps:

and 41, keeping the frequency conversion control signal as a first duty ratio and a first frequency.

And 42, acquiring zero-crossing points of the voltage and the current of the first alternating current power supply to calculate a detection phase difference theta a of the voltage and the current of the first alternating current power supply, and calculating a detection power factor FW according to the detection phase difference theta a, wherein the detection power factor FW is cos (theta a).

In step 43, it is determined whether the target power P _ set is changed.

Step 44, when the target power P _ set is changed, PID power regulation is executed; when the target power P _ set is not changed, a second difference F1 between the detected power factor FW and the maximum power factor is judged.

Step 45, when the second difference value F1 is within a first preset power factor range PFrf, performing PID power regulation; when the second difference F1 is within the first preset power factor range PFrf, the duty ratio of the updated control signal is adjusted according to the phase difference between two adjacent time periods before the current time period.

Specifically, a phase difference Δ θ between a detected phase difference θ a and an ideal phase difference θ B is obtained, where Δ θ is a × θ (t) -B × Δ θ (t-1) + C × Δ θ (t-2), and a Δ duty ratio is D × Δ θ, where D is a constant, and at a time t-1, Δ θ (t-1) is Δ θ (t); at time t-2, Δ θ (t-2) ═ Δ θ (t-1). Then, in the t +1 time period, the duty ratio (t +1) of the control signal is equal to the duty ratio (t) + Δ duty ratio of the control signal.

And step 46, when the microwave frequency conversion circuits 10 and 20 have abnormal conditions, executing the protection logic 5.

Through PID power regulation and PID power factor dynamic regulation and correction, the input power of the first alternating voltage is enabled to be close to the target power quickly, and overshoot or oscillation can be effectively avoided.

Specifically, referring to fig. 8 and 13 together, fig. 13 is a flowchart illustrating a specific step of executing the protection logic in step 5 when the magnetron shown in fig. 8 is abnormal.

As shown in fig. 13, the executing protection logic at least includes the following steps:

and step 51, detecting and acquiring the voltage Urms and the current Irms of the first alternating current power supply, and acquiring the temperatures of the IGBT and the

magnetrons

17 and 27 in the frequency conversion control unit 121.

And step 52, entering a protection logic state 50 when the temperature of the IGBT and the magnetron exceeds a threshold temperature Tth.

And step 53, when the temperature of the IGBT and the magnetron does not exceed the threshold temperature Tth, determining whether the voltage Urms of the first alternating current power supply exceeds a voltage threshold range.

Step 54, protecting the logic state 50 when the voltage of the first ac power source Urms exceeds the voltage threshold range; when the voltage of the first ac power supply Urms does not exceed the voltage threshold range, it is determined whether the current Irms of the first ac power supply is within the overcurrent threshold range Ith.

When the current Irms of the first ac power source exceeds the overcurrent threshold range Ith, the protection logic 50 is executed; when the current Irms of the first ac power supply does not exceed the overcurrent threshold range, it is determined whether the number of times of jitter of the current Irms of the first ac power supply is within the jitter threshold range.

Step 55, when the jitter frequency of the current Irms of the first ac power exceeds the jitter threshold range, entering the protection logic state 50; if the jitter threshold is exceeded, then normal operation is performed 56.

And step 50, entering a protection logic state, specifically, stopping outputting the control signal by the

control units

16 and 26, so that the inverter circuit stops inverting voltage-multiplying conversion, thereby protecting the microwave frequency conversion circuits 10 and 20.

Accordingly, the warm-up state in step 1 and the subsequent steps are resumed when the abnormal situation is eliminated.

Compared with the prior art, the voltage and the phase of the first alternating current power supply received by the alternating current input end Vin are detected directly, so that the voltage and the zero crossing point of the first alternating current power supply can be obtained more accurately, the phase difference between the voltage and the current of the first alternating current power supply is accurately identified, and more accurate power factor adjustment is carried out to the maximum value according to the phase difference.

Further, the voltage and the current of the first alternating current power supply are accurately identified, and more accurate proportion forward regulation and PID power regulation of the first alternating current voltage are further obtained, so that power regulation and power factor correction of the multiple closed-loop self-

adaptive magnetrons

17 and 27 are formed, and the stability, the safety and the reliability of the microwave frequency conversion circuits 10 and 20 are effectively improved.

Further, the first protection unit 28 is arranged to accurately detect the current in the first dc power supply, so as to accurately identify whether the abnormal conditions such as short circuit and overcurrent exist in the loop of the first dc power supply, and thus, the protection logic can be executed when the abnormal conditions occur, and the microwave frequency conversion circuits 10 and 20 are prevented from being damaged.

Furthermore, the current and the temperature of the

magnetrons

17 and 27 are detected, so that the protection logic is executed in time when the abnormal conditions caused by overcurrent and overvoltage during the operation of the

magnetrons

17 and 27 are accurately identified.

The above-described embodiments do not limit the scope of the present invention. Any modification, equivalent replacement, and improvement made within the spirit and principle of the above-described embodiments should be included in the protection scope of the technical solution.

Claims

1. A microwave frequency conversion circuit, comprising:

the control circuit is electrically connected to the power conversion control circuit, the first voltage detection circuit and the first current detection circuit, the control circuit identifies a phase difference between zero-crossing points in the phases of the voltage and the current according to the first voltage detection signal and the first current detection signal, and outputs the control signal according to the phase difference to correct the power factor of the first ac power source, wherein correcting the power factor of the first ac power source includes adjusting a duty cycle of an update control signal, and adjusting the duty cycle of the control signal includes:

acquiring a phase difference delta theta between a detected phase difference (theta a) and an ideal phase difference (theta B), wherein delta theta is A, theta (t) -B, delta theta (t-1) + C, delta theta (t-2), a delta duty ratio D, delta theta, A, B, C, D is a constant, and delta theta (t-1) is delta theta (t) at a time t-1; at time t-2, Δ θ (t-2) is Δ θ (t-1), and the duty ratio (t) of the control signal corresponding to the adjusted t time period is the duty ratio (t-1) + Δ duty ratio of the control signal.

2. A microwave frequency conversion circuit according to claim 1,

the first voltage detection unit comprises a first voltage detection circuit and a zero-crossing detection circuit;

the first voltage detection circuit includes:

the first detection end and the second detection end are respectively and electrically connected with the first input end and the second input end;

the first differential operational amplifier comprises a first in-phase input end, a first reverse phase input end and a first amplification output end, wherein the first in-phase input end is electrically connected with the first detection end through at least one first detection resistor, the first reverse phase input end is electrically connected with the second input end through at least one second detection resistor, the first reverse phase input end is electrically connected with the first amplification output end through a feedback amplification unit, and the feedback amplification unit comprises a first feedback resistor and a first feedback capacitor which are mutually connected in parallel;

the first differential operational amplifier converts the first alternating current power supply into a sinusoidal first voltage detection signal according to a first proportion, and the first voltage detection signal represents the voltage of the first alternating current power supply.

3. A microwave frequency conversion circuit according to claim 2,

the zero-crossing detection circuit comprises a zero-crossing comparator, the zero-crossing comparator comprises a second non-inverting input end, a second inverting input end and a first comparison output end,

the second in-phase input end is electrically connected with the first amplification output end through a third detection resistor, and the second in-phase input end is electrically connected with the first comparison output end through a second feedback resistor;

the second inverting input end is electrically connected with the first reference voltage through a fourth detection resistor;

the first comparison output end is electrically connected with a second reference voltage, the first amplification output end is used for outputting a first square wave pulse signal, and the first square wave pulse signal and the first voltage detection signal have the same phase and are used for representing a zero crossing point of the first voltage detection signal.

4. The microwave frequency conversion circuit according to claim 1, further comprising a first protection unit for detecting a high-side current in the first dc power source output by the rectification circuit, wherein when the high-side current exceeds a high-side threshold current, the control circuit controls the inverter circuit to stop converting the first dc power source into the second ac power source.

5. A microwave frequency conversion circuit according to claim 4,

the first protection unit comprises a first shunt resistor, and the first shunt resistor is electrically connected between the rectifying circuit and the inverter circuit; or,

the first protection unit comprises a first current mutual inductance element, and the first current mutual inductance element is electrically connected between the rectifying circuit and the inverter circuit.

6. A microwave frequency conversion circuit according to claim 1,

the microwave frequency conversion circuit further comprises a first feedback detection unit, the first feedback detection unit is electrically connected to the magnetron and used for detecting the current of the magnetron, and when the current of the magnetron exceeds a load current threshold, the control circuit controls the inverter circuit to stop converting the first direct current power supply into the second alternating current power supply.

7. A microwave frequency conversion circuit according to claim 6,

the inverter circuit comprises a transformer and a voltage doubling circuit electrically connected with the transformer;

the transformer comprises a primary winding, a first secondary winding and a second secondary winding, the primary winding receives the first alternating current power supply, and the first secondary winding is electrically connected with the cathode of the magnetron;

the voltage doubling circuit comprises a first high-voltage diode, a second high-voltage diode, a first high-voltage capacitor and a second high-voltage capacitor which are connected between the second secondary winding and the anode of the magnetron;

the first feedback detection unit comprises a second shunt resistor, wherein the second shunt resistor is electrically connected between the second high-voltage capacitor and the ground terminal, or

The first feedback detection unit comprises a second current mutual inductance element, wherein the second current mutual inductance element is electrically connected between the first high-voltage capacitor and the second high-voltage capacitor.

8. The microwave frequency conversion circuit according to claim 1, further comprising a temperature sensing unit for sensing a temperature of the magnetron and feeding back the detected temperature to the control circuit, wherein the control circuit controls the inverter circuit to stop converting the first dc power supply into the second ac power supply when the temperature of the magnetron exceeds a load temperature threshold.

9. The microwave frequency conversion circuit according to any one of claims 1 to 8, further comprising a communication circuit electrically connected to the control circuit, wherein the control circuit transmits the state of the microwave frequency conversion circuit to an external circuit through the communication circuit.

10. A method for controlling a microwave frequency conversion circuit according to any one of claims 1 to 9,

receiving the first alternating current power supply from the alternating current input end, converting the first alternating current power supply into the first direct current power supply, converting the first direct current power supply into the second alternating current power supply by inversion voltage doubling, supplying power to the magnetron, and simultaneously controlling the power of the second alternating current power supply through the control signal;

performing PID power factor adjustment for the first AC power source, the PID power factor adjustment comprising:

and when the second difference value is within a first preset power factor range, adjusting the duty ratio of the updating control signal so as to adjust the power factor of the first alternating current power supply.

11. The method for controlling a microwave inverter circuit according to claim 10, further comprising, before obtaining the zero-crossing point of the voltage and the zero-crossing point of the current of the first ac power source, the steps of:

and keeping the frequency conversion control signal at the first duty ratio and the first frequency.

12. The control method of a microwave frequency conversion circuit according to claim 10,

the method also comprises the preheating step when the first direct current power supply is converted into a second alternating current power supply according to the inversion voltage doubling to supply power to the magnetron:

providing a control signal with a first duty ratio and an initial frequency, and converting the first direct current power supply into a second alternating current power supply according to the time length of the first duty ratio and the initial frequency according to the control signal, so that the first direct current power supply is converted into the second alternating current power supply according to a first resonant frequency;

detecting and acquiring the voltage and the current of the first alternating current power supply, and calculating first alternating current input power according to the voltage and the current of the first alternating current power supply;

when the first alternating current input power is larger than the preheating power, increasing the frequency of a control signal according to a fixed step length, and when the first alternating current input power is smaller than the preheating power, reducing the frequency of the control signal according to the fixed step length;

and when the first alternating current input power is equal to the preheating power, judging whether the preheating time is longer than a preset time length, and when the preheating time is longer than the preset time length, representing that the preheating of the magnetron is finished.

13. The method for controlling a microwave frequency conversion circuit according to claim 12,

when the preheating time is longer than the preset time, the step of carrying out the forward regulation of the input power according to the proportion comprises the following steps:

judging the magnitude of the first alternating current input power and a preset target power;

when the first alternating current input power is larger than or equal to a preset target power, completing the forward adjustment of the input power proportion;

and when the first alternating current input power is smaller than a preset target power, reducing the frequency of the control signal according to a fixed step length.

14. The method of claim 13, wherein the step of performing PID power adjustment after the input power reaches the preset target power through proportional forward adjustment comprises:

judging whether a first difference value between the first alternating current input power and a preset target power is within a first threshold range or not;

performing a PID power factor adjustment when the first difference is within a first threshold range;

and when the first difference exceeds a first threshold range, adjusting the frequency of the control signal according to the first difference of two adjacent time periods before the current time period.

15. A control method of a microwave frequency conversion circuit according to any one of claims 11 to 14, characterized in that the specific steps of the protection logic are executed when an abnormal condition occurs in the magnetron in any one of the steps:

acquiring the voltage and the current of the first alternating current power supply, and detecting the temperature of a variable frequency control unit and the temperature of the magnetron;

when the temperature of the variable frequency control unit and the magnetron exceeds the threshold temperature, entering a protection logic state;

when the temperature of the variable frequency control unit and the temperature of the magnetron do not exceed the threshold temperature, judging whether the voltage of the first alternating current power supply is within the voltage threshold range;

when the voltage of the first alternating current power supply exceeds the voltage threshold range, entering a protection logic state;

when the voltage of the first alternating current power supply does not exceed the voltage threshold range, judging whether the current of the first alternating current power supply is in an overcurrent threshold range;

entering a protection logic state when the current of the first alternating current power supply exceeds an overcurrent threshold range;

when the current of the first alternating current power supply does not exceed the overcurrent threshold range, judging whether the jitter frequency of the current of the first alternating current power supply is in the jitter threshold range;

when the jitter frequency of the current of the first alternating current power supply exceeds the jitter threshold range, entering a protection logic state;

and entering a protection logic state, including stopping outputting the control signal to control the first direct current power supply to stop converting into the second alternating current power supply.